Clinical, electrophysiological, and anatomical studies indicate that the posterior parietal cortex of man and monkeys is important for visual-spatial perception. This proposal is a combined neurophysiological and neuroanatomical study which is designed to investigate how aspects of visuospatial perception might be encoded by the light-sensitive cell class of this region. This proposal has three specific aims: 1) to study the spatial interactions of visual stimuli in the large receptive fields of the light-sensitive neurons, 2) to study the effect of position of the eyes and head on light sensitivity, and 3) to study the functional anatomy of Area 7 with particular emphasis on the organization of visuospatial properties. These aims will be achieved by recording the activity of single neurons from the posterior parietal cortex of behaving monkeys. The experimental animals will be trained to perform tasks designed to elucidate visuospatial properties of the light sensitive cells. Microelectrode mapping experiments will be combined with neuroanatomical tracing experiments to define functional subdivisions within this region and the local callosal and ipsilateral cortico-cortical inputs and outputs of these subdivisions. Data analysis will include the reconstruction of the population response of this region. Using the posterior parietal lobe as an example, inferences will be made of the role of homotypic cortex in higher functions.